Contoured PCD and PCBN segments for cutting tools containing such segments

ABSTRACT

Contoured helical solid polycrystalline PCD and PCBN superabrasive segments are provided for attachment to cutting tool substrates such as twist drill tips, reamers, burrs and endmills. Segments are provided in near to net shape for attachment to a tool substrate thereby requiring reduced finishing steps and providing increased tailorability of grade and quality of final polycrystalline segments. Cutting tools comprising cutting tool substrates having attached thereto a contoured helical solid polycrystalline PCD and PCBN superabrasive segments are also disclosed.

RELATED APPLICATION

This application is a continuation-in-part of allowed U.S. applicationSer. No. 11/732,712 filed Apr. 3, 2007, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to cutting tools andparticularly to superabrasive contoured helical segments for attachingto or inserting into cutting tool substrates such as drill bits,reamers, burrs and end mills. Thus, the invention involves the fields ofcutting tools, superabrasive materials, materials science, andmetallurgy.

BACKGROUND OF THE INVENTION

Polycrystalline superabrasive materials like PCD and PCBN have beenwidely used for years in both metalworking and woodworking industries byvirtue of their unique mechanical and physical properties. Thesesuperabrasive materials tend to have a high abrasive resistance, hightoughness, and high hardness. However, these superabrasive materialshave not been effective in other cutting tool industry especially inmilling and drilling applications due primarily to availability and costfactors.

The main drawback is related to the unique design or shape of toolproducts in which the cutting face of PCD or PCBN is fluted or helicalshaped for an effective cutting performance. Unfortunately, helicalshapes are not readily fabricated from PCD or PCBN under HPHT sinteringprocess due to complexity in cell designs in combination with theirsuperhard material characteristics. Furthermore, any conventionalshaping process in an attempt to put the flute or helical shape into asuperabrasive material by finishing operations such as grinding is avery tedious and costly process. This is true even with superabrasiveparts having a nearly net shape of a desirable final product design.

Historically, one main barrier preventing diamond or PCD tools frompenetrating the market against conventional tool materials like eitherhigh speed steel or carbide has been the manufacturing cost. Currently,veined PCD drills made according to U.S. Pat. No. 5,580,196 of AbrasiveTechnology is an upgrade product over electroplated CVD coated orfabricated drills especially in aerospace and automotive industry.However, it has been reported that product life of these materials isshort from failing fabrication joints and a lack of a rugged edge. Inaddition, the price of this tool is very expensive so that manypotential consumers are reluctant to try.

U.S. Pat. No. 6,158,304 to Smith International, Inc. teaches a centercutting end mill having spiral grooves and flutes in the end millsubstrate filled with polycrystalline diamond or cubic boron nitrideformed or sintered in situ in the grooves to integrally bond via partialinfiltration into the substrate. The PCD or PCBN materials as bonded inthe grooves is then subsequently ground to a final shape by conventionaltechniques such as by grinding, wire electrical discharge cutting (EDM)or electrical discharge grinding (EDG). This process requires that themill body and PCD or PCBN material both be subjected to high pressure,high temperature conditions and then the bonded PCD or PCBN be furtherreshaped to form a cutting edge.

Megadiamond has introduced carbide inserts with veins of PCD but whichare only one inch long which requires a braze point to a carbiderod/shank of the same diameter. However, this is a mechanical weaknessand makes flute grinding difficult, especially on automated grinders.Another weakness of these veined PCD end mill cutters is that theycannot resharpen an expensive tool because the PCD insert is tooshallow. In short, although some progress has been made in the past fewyears, the rotary tool market within the cutting tool industry has longdesired both the helical or fluted PCD drill tip and a reliable PCDfluted end mill that are cost competitive and reliable in toolperformance over the existing superabrasive tools.

SUMMARY OF THE INVENTION

This invention relates to a new helical shaped solid PCD and PCBN tipsegments that can be attached or inserted into the conventional toolsubstrates such as twist drills, drills, reamers, burrs and end mills.Contoured segments, such as the helical PCD twist drill tip materials ofthe present invention are significantly improved in both product designand material versatility. Furthermore, the manufacturing cost of a finaltool is cheaper than conventional PCD tips at least partially due toproduction of near to net shaped tip segments using the methods of thepresent invention. More importantly, the manufacture of helical/flutedPCD and PCBN segments is relatively easier to fabricate under HPHTprocess. Therefore, the present invention overcomes many ofdisadvantages associated with current HPHT PCD sintering and follow-upproduct shape forming processes.

The present invention, as described herein, allows a number ofachievements in making contour helical shaped polycrystalline PCD orPCBN segments to be applied for a variety of drilling and milling toolssuch as a tip for rotary diamond tools including, but not limited todrills, reamers, burrs, and endmills. For example endmills can includeend- and face-milling tools such as flat bottom, ball nose, radius,inverted radius, and chamfer tools. However, the detailed portions willbe described herein primarily in terms of PCD or PCBN drill tip segmentsand endmill segments. The application of the principles as describedherein can readily be applied to other segments for reamer, burrs andthe like by one skilled in the art. The contoured helical PCD drill andfluted endmill segments of the present invention can be a viablealternative for existing products in drilling and milling applicationsfor the cutting tool industry. Accordingly, the present inventionprovides materials and methods for manufacturing of ultrahard materialsegments and fabrication by attachment to tool substrates which are farbetter in both quality and utility and more cost effective thancomparable conventional materials.

In accordance with one aspect of the present invention, a helical PCD orPCBN twist drill tip segments can be a solid PCD or PCBN with no metallayer backing. The end mill tip segments can also be either helicalsolid PCD or PCBN material. In another aspect of the invention, thesehelical segments can also have a carbide tip cemented thereon to providea less brittle outer tip working surface.

The solid contoured PCD and PCBN segments of the present invention canbe formed by a method which includes charging reaction cup assembly witha specially prepared powder form of ultrahard materials (diamond or CBN,sintering aids, bonding medium, etc.). This reaction cup assembly can beformed of precursors which include molds having several helical shapedspaces to be occupied by the ultrahard materials and associatedsintering aids. The form material can be made of materials such asgraphite, MgO, salt, HBN, etc. In some aspects of the present invention,the superabrasive starting materials can be either crushed PCD materialor agglomerated diamond material. The cup assembly having the shapedprecursor feed charge can be loaded in a conventional HPHT cell andsubjected to a pressure, temperature and time conditions suitable fordiamond synthesis or PCD/PCBN sintering.

In another aspect of present invention, solid PCD or PCBN segments canbe manufactured from a near-to-shape solid PCD or PCBN from HPHTpressing by a modified method of cutting and grinding operations.

The contoured and helical shaped solid polycrystalline superabrasivesegments of the present invention can be useful attachments or insertsfor a broad range of rotary diamond cutting tool substrates in bothmetalworking and woodworking industries, and especially for drilling andmilling for both ferrous and nonferrous materials where conventionaltools like HSS and WC tools (drills, end mills, reamers and the like)are dominant but not performance-effective at the present time.

The cutting segment products of the present invention are economicallyand technically viable products when compared to existing PCD relatedtools being commercialized currently even in limited amounts. Themethods of the present invention are technically reliable and tailorablein making various sizes and product grades that have so far beentechnically limited by current manufacturing processes. Therefore, theutility of segment products made in accordance with the presentinvention can be much broader and easily offered to meet market demands.A final cutting tool using these new segments attached to a toolsubstrate is manufactured more cost effectively, requiring much lessgrinding time, for example, in CNC grinding during final toolfabrication.

Further benefits to current cutting tool industry can be provided in away that a flexibility of tool designs with both helical (fluted) PCDand PCBN contoured segment containing drills and endmills can beutilized in much broader application areas like aircraft and automotiveindustries. In addition, the methods of the present invention offer awide selection of PCD and PCBN grades that are suitable for everincreasing demand for newly developed workpiece shapes and materials.

There has thus been outlined, rather broadly, the more importantfeatures of the invention so that the detailed description thereof thatfollows may be better understood, and so that the present contributionto the art may be better appreciated. Other features of the presentinvention will become clearer from the following detailed description ofthe invention, taken with the accompanying drawings and claims, or maybe learned by the practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a precursor mold having multiple helical shaped openingscorresponding to multiple contoured helical drill tip segments that willbe filled with specially prepared diamond powder for sintering PCD orPCBN of near-to-shape solid body and a set of caps which cover thepowder particulate feed charge to provide an upper surface shape inaccordance with one embodiment of the present invention.

FIG. 2 shows a precursor mold having multiple openings of contouredhelical shape endmill tip segments and corresponding cylindrical discand base for surrounding the mold in accordance with another embodimentof the present invention.

FIG. 3 is a perspective view of a final contoured PCD helical drill tipsegment removed from the mold of FIG. 1 in accordance with anotherembodiment of the present invention.

FIG. 4 shows an ideal contoured helical shape PCD or PCBN endmillcutting edge segment removed from the mold of FIG. 2 after sintering inaccordance with another embodiment of the present invention.

FIG. 5 shows a perspective view of a helical PCD drill having acontoured helical solid PCD tip segment brazed thereon in accordancewith one embodiment of the present invention.

FIG. 6 shows a perspective view of a contoured helical PCD endmillhaving a helical solid PCD endmill blade segment brazed thereon inaccordance with one embodiment of the present invention.

The drawings will be described further in connection with the followingdetailed description. Further, these drawings are not necessarily toscale and are by way of illustration only such that dimensions andgeometries can vary from those illustrated.

DETAILED DESCRIPTION

Before the present invention is disclosed and described, it is to beunderstood that this invention is not limited to the particularstructures, process steps, or materials disclosed herein, but isextended to equivalents thereof as would be recognized by thoseordinarily skilled in the relevant arts. It should also be understoodthat terminology employed herein is used for the purpose of describingparticular embodiments only and is not intended to be limiting.

It must be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a precursor” is not to be taken as quantitatively orsource limiting and reference to “a charging step” or “heating step” mayinclude multiple steps.

DEFINITIONS

In describing and claiming the present invention, the followingterminology will be used in accordance with the definitions set forthbelow.

As used herein, “contoured” refers to surfaces which are non-planarhaving curved topology. Typically, the products of the present inventioninclude helically contoured segments, although other curved shapes canalso be suitable for some tool applications Therefore, all segmentsaccording to the present invention are “contoured” and, in certainembodiments, the contoured shape will be helical. Unless otherwisespecified the terms contoured, helical and spiral can be usedinterchangeably.

As used herein, “superabrasive” refers to abrasive materials which areultrahard such as diamond, CBN and polycrystalline diamond (PCD) or CBN(PCBN). Further, the terms superabrasive and PCD are often usedinterchangeably herein unless the context specifically indicatesotherwise.

As used herein, “inorganic bonding medium” refers to a material whichacts as a matrix for sintering or as a filler material in which diamondparticles are dispersed. Typically, the bonding medium can chemicallybond with the sintering aid and/or diamond particles, although somemechanical bonding is often also present.

As used herein, “precursor” refers to a mass prior to a relevant action.For example, a charged precursor includes raw particulate materialsprior to subjection to HPHT sintering conditions.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

As used herein, “about” refers to a degree of deviation based onexperimental error typical for the particular property identified. Thelatitude provided the term “about” will depend on the specific contextand particular property and can be readily discerned by those skilled inthe art. The term “about” is not intended to either expand or limit thedegree of equivalents which may otherwise be afforded a particularvalue. Further, unless otherwise stated, the term “about” shallexpressly include “exactly,” consistent with the discussion belowregarding ranges and numerical data.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 4 percent to about 7percent” should be interpreted to include not only the explicitlyrecited values of about 4 percent to about 7 percent, but also includeindividual values and sub-ranges within the indicated range. Thus,included in this numerical range are individual values such as 4.5, 5.25and 6 and sub-ranges such as from 4-5, from 5-7, and from 5.5-6.5, etc.This same principle applies to ranges reciting only one numerical value.Furthermore, such an interpretation should apply regardless of thebreadth of the range or the characteristics being described.

Embodiments of the Invention

The present invention encompasses methods of making a contoured solidpolycrystalline superabrasive segment which can be attached to orinserted into a drill bit, end mill or other cutting tool substrate.Referring now to FIG. 1 a precursor mold 10 can be prepared having aplurality of shaped openings 12 each corresponding to a predeterminedsegment shape. The precursor mold can be formed by any suitabletechnique such as, but not limited to, casting, molding, 3D printing,carving of a solid material e.g. by laser or wire EDM, or other suitablemanufacturing techniques. The precursor mold can comprises or consistessentially of a material selected from the group consisting ofgraphite, hexagonal boron nitride, alumina, ceramics, composites oralloys thereof or combinations of these materials. The choice of moldmaterial can depend on the type of polycrystalline material beingformed, rigidity, cost, or the like. For example, graphite molds can bepreferred for formation of PCD materials while hBN molds can bepreferred for formation of PCBN. Optionally, the precursor mold canfurther include sintering aids which can diffuse into the particulatecharge feed during sintering. However, generally any material havingsufficient mechanical strength to resist excessive deformation orshrinkage during HPHT processing can be used, e.g. salt, talc and orother materials can be useful in some embodiments.

The mold can be designed to include shaped openings having any number ofpredetermined segment shapes. FIG. 1 illustrates predetermined shapescorresponding to a helical shaped drill tip segment. Generally, thehelical shaped segment can be a drill bit tip segment twisted about acentral axis of rotation by about 5° to about 40° from planar, andpreferably about 8° to about 20°. Edges of the drill tip segment can becontoured so as to blend with contours of a corresponding fluting on adrill bit body. In order to form a tip portion of the tip segment, moldcaps 14 can be oriented over the particulate charge feed 16 in order tofurther shape the particulate material. Regardless of the particularpredetermined shape, the predetermined shape is typically slightlylarger than the desired final shape in order to compensate for shrinkageduring sintering.

FIG. 2 illustrates another embodiment of the present invention where theprecursor mold 20 includes shaped openings 22 corresponding to a helicalend mill fluting segment. In this case an annular sheath 24 and topplate 26 can provide convenient cup assembly walls to confine theparticulate charge feed by placing the precursor mold within the sheathand covering the mold with the top plate. In this case the precursormold can be made of materials as discussed previously, while the sheathand top plate can be formed of suitable refractory metals such as Ti,Mo, etc.

A specially prepared charge feed can be placed into the shaped openingsto form a shaped charge feed within a charged precursor (i.e. the moldprecursor plus the charge feed). The specific composition andconfiguration of the charge feed can be readily tailored for formationof a polycrystalline superabrasive material having a desired quality andproperties. As a general matter, the charge feed can include, or consistessentially of, a substantially homogeneous mixture of superabrasivesource particulates, sintering binder, and optional inorganic bondingmedium.

The superabrasive source particulates can include diamond, CBN, PCBN,polycrystalline diamond, or any other material which acts as a sourcematerial for superabrasive material, i.e. diamond sinters to form PCDand CBN sinters to form PCBN. In one alternative embodiment, thesuperabrasive particulates are crushed polycrystalline powders producedby crushing of polycrystalline diamond or polycrystalline boron nitride.These polycrystalline particulates can be prepared from crushing oftypical PCD that is selected for the desirable properties of the finaltool. In another embodiment, the diamond particulate powder for the feedcharge can be preprepared to be somewhat coarser in size from a typicalpowder agglomeration process in order to improve the powder packingefficiency in loading into the precursor. For example, 40/50 mesh toabout 300/400 mesh can be combined to prepare bimodal or trimodal feedcharges, although up to about 10/20 mesh can be used. An original powderformed from a mixture of various fine diamond powder sizes combined witha bonding medium as well as a sintering aid like cobalt with a presenceof organic binders like wax for easy forming into a suitable round mold(e.g. a refractory metal cup like Ti or Mo). The preform of this initialdiamond feed mixture is then dewaxed followed by heat treatment at1100-1200° C. for 30 minutes under a high vacuum state to form anagglomerate. In the agglomerate, the diamond or CBN is typically notsintered; however, the sintering aid melts and flows to form a cementingmatrix around the unsintered particles. It can then be crushed into theagglomerate particles of rather coarse sizes such as 30-80 meshparticulates. The initial diamond powder size (0.5-400 microns), diamondvol. % (30-90 vol. %), binder concentration (50%-1 vol %), bondingmedium (like carbide powder) concentration can be varied in a broaderrange depending on the desired final PCD product properties. Forexample, a tougher PCD can have 65 vol % to 99 vol %, while a softer PCDcan have less than 60 vol % diamond. The crushed particles of eitherpolycrystalline or agglomerates can be substantially free of metal.Removal of metals can be accomplished by acid leaching or other suitableapproaches.

The specially prepared charge feed can further be configured in order toincrease packing density and reduce void space. In one currentlypreferred embodiment, the charge feed can include a trimodaldistribution of superabrasive particles. For example, a trimodal mixtureof 40/50 mesh, 100/120 mesh and 230 mesh superabrasive sourceparticulates can provide good results. As a general rule, the diamond orsuperabrasive source particles can have almost any useful size.Typically, the diamond particles can have a size from about 0.5 μm toabout 500 μm, and although other sizes can also be used. For example,120 to 200 μm diamond can facilitate production of larger PCD segmentshaving a high quality and uniform sintering throughout.

The diamond content of the particulate feed charge can be from about 30vol % to about 95 vol %, and preferably from about 50 vol % to about 90vol %. Although in some cases it can be desirable to include significantportions of filler material such as bonding medium or other materials.

The sintering aid can be any material which acts to facilitate sinteringunder HPHT conditions. Non-limiting examples of sintering aids fordiamond can include Co, Ni, Fe, Mn, Cr, and alloys thereof with Fe, Niand Co being currently preferred. Non-limiting examples of sinteringaids for cubic boron nitride can include an alkali metal nitride,alkaline earth metal nitride, Al—Si alloys and the like. For example,lithium, calcium, magnesium, and nitrides of alkali and alkaline earthmetals such as Li₃N, Ca₃N₂, and Mg₃N₂ can be useful as sintering aidsfor PCBN. Typically, the sintering aid can be present in the particulatefeed charge at about 1 vol % to about 30 vol %.

Non-limiting examples of suitable bonding medium materials can compriseor consist essentially of, cubic boron nitride, tungsten carbide, boron,silicon nitride, tantalum carbide, silicon carbide, alumina,combinations thereof, and the like. The inorganic bonding medium can beany material which provides sufficient hardness and acts as a medium forbonding of the diamond particles in fixed positions relative to oneanother and can affect the final PCD thermal stability, toughness andhardness. As a general guideline, inorganic bonding medium that providessufficient hardness and acts as a medium for bonding of the diamondparticles can be present in the particulate feed charge from about 1vol. % to about 20 vol. % and preferably from about 2 vol. % to about 15vol. %. In one specific embodiment, the inorganic bonding medium can betungsten carbide powder that can typically have a size from about 0.5micron to about 20 microns.

In some cases, it can be desired to have the tip of a cutting segment,such as shown in FIGS. 3 and 4, that is less brittle when placed in atool substrate, as shown in FIGS. 5 and 6. As such, a tip portion of thecutting segment can provide leading work surfaces which are a toughbuffer between more brittle superabrasive and impact with a work piece.The tip portion can typically be formed of a carbide material which hasa lower hardness and higher toughness than the segment body. The tipportion can comprise the initial contact surfaces with a work piece. Forexample, a composite tip portion in FIG. 3 may measure from about 5% toabout 35% of the total segment height. The particulate feed charge, formaking the tip as described below, can be made up of a compositecomprising 30-95% vol. % tungsten carbide (WC), 5 to 20 vol. % of asintering aid comprising Co, Ni or Fe; and 0 to 50 vol. % of aparticulate abrasive comprising PCD or PCBN particles. Although WCprovides strong tip portions, other metal carbides or nitrides can alsobe suitable such as transition metal carbides and nitrides. Non-limitingexamples of such materials can include WC, TiC, TaC, NbC, TiN, ZrN, HfN,VN, NbN, and combinations thereof. Additionally, superabrasive can beoptional in the tip portion, although such material can help to increasehardness and provide faster cutting performance. The particulate feedcharge will be placed in the mold openings as described below prior tothe homogeneous mixture of superabrasive particulates, sintering binder,and optional inorganic bonding medium as previously described. Theresulting segment subjected to HPHT treatment in the mold will have acarbide cutting tip cemented to the remainder of PCD or PCBN segmentbody. For segments where a cutting tip segment is desired that is not ashard and less brittle this embodiment will provide such features.

Regardless of whether the feed charge is homogeneous or formulated tohave a composite carbide tip, the particulate feed charge can then beplaced into the shaped openings of precursor to form a chargedprecursor. The reaction cup assembly comprises the uniquely made moldprecursor having multiple desirably shaped (e.g. helical) partitions oropenings conforming to the contour shape of the segment being produced.The precursor mold is loaded with the diamond particulates by fillingthe openings. Suitable caps, plates or other members can be used tofully encapsulate the charged particulate material. The chargedprecursor can then be prepared to form a reaction cup-assembly suitablefor use in a HPHT apparatus. The charged precursor can be directlyplaced in a HPHT apparatus or prepared by including various conventionalgaskets, cup layers, and the like.

The loaded reaction cup-assembly can then be subjected to a pressure,temperature and time sufficient for sintering and formation of thecontoured polycrystalline superabrasive material into the desiredsegment shape. Any suitable HPHT apparatus can be used such as, but notlimited to, piston-cylinder, multi-anvils, belt devices, and any othersuitable high pressure press. Although specific conditions can vary,depending on the feed charge composition, the temperature of typicalPCD/PCBN sintering is from about 1250° C. to about 1450° C. and thepressure is from about 40 kb to about 55 kb. Typical sintering time oncethe sintering temperature is reached is from about 1.0 minute to about30 minutes.

Subsequent to sintering, the contoured polycrystalline superabrasivematerial segments can be removed from the HPHT apparatus and from thecup assembly. This can be done by mechanical breaking of the precursormold and/or chemical rinsing to dissolve non-polycrystalline portions ofthe pressed mass. The recovered segments are typically near net shapeand often require little or no further finishing for practical use. Forexample, the precursor mold 10 of FIG. 1 results in contoured drill bittip segments as illustrated in FIG. 3. Similarly, the precursor mold 20of FIG. 2 results in a contoured endmill flank segment as shown in FIG.4.

In some cases the contoured polycrystalline superabrasive material canbe further finished by grinding and cutting to form a final helicalshape drill bit tip or end mill segment. This typically involves onlyminor material removal in order to polish edges, remove extraneousartifacts, and/or to fine tune fit for a particular tool substrate.

Alternatively, the predetermined contoured shape can be configured so asto produce pieces which are not near net shape, but rather requireadditional grinding and cutting operations to form the final toolsegment. This may be particularly true when the segment produced has atungsten carbide tip. However, such pieces still require significantlyless finishing steps to produce a contoured helical solid PCD thanconventional grinding from a solid blank PCD.

In accordance with the present invention, the contoured polycrystallinesuperabrasive material can have a superabrasive content of about 90 vol.% to about 98 vol. %, and generally about 30 vol. % to about 98 vol. %.As mentioned previously, the methods of the present invention allow formuch greater control over product grade and quality at least partiallyby improving pressure distribution throughout the precursor during HPHTconditions. It has been an inherent process drawback for typical HPHTPCD sintering method to produce odd shapes like contoured helical PCDusing a conventional cell design. Poorly sintered PCD would result fromweak bond strengths between diamond grains (diamond-to-diamond ordiamond-to-medium grain). In other words, the weak bond strength isbelieved to be due to insufficient local pressure at the grain boundaryof diamonds in PCD during HPHT sintering. This is in turn due todifficulties in achieving the necessary packing of diamond powder in thereaction-cup when varying geometry from a standard blank or supportedPCD during the HPHT sintering. Consequently, the resultant pressureapplied into the localized grains under a conventional HPHT cellassembly is not sufficient enough to maintain desirable HPHT reactionconditions at the grain interfaces for proper diamond-to diamond bondingsuch that the overall PCD quality is poor.

The finished contoured segments of the present invention can optionallybe further treated in order to improve bonding with a desired toolsubstrate, e.g. a tip of a fluted drill bit shank or flanks of an endmill shank. For example, the contoured polycrystalline superabrasivematerial can be coated with a brazeable carbide or nitride formingmaterial. Suitable brazeable materials can include, but are not limitedto, transition metals (e.g. Co, Cr, Ni, Ta, Ti, W, Mo, etc.), steels,and their alloys.

In another optional aspect of the present invention, the contouredpolycrystalline superabrasive materials can be acid leached in order toremove residual metals. This can increase the high temperature thermalstability of the material by removing and/or reducing the amount ofresidual sintering aid present in the material which may act tobackconvert diamond to graphite under high temperature drilling ormilling.

The final contoured segments can then be brazed or otherwise attached toa suitable tool substrate. FIG. 5 illustrates a two-fluted drill bitshank 50 having a contoured drill bit tip 52 set into a preformed groovenear the tip of the shank. In this embodiment the tip segment 52 is alsoshown separately where the side edges 54 are shaped so as to blend intoand match the contours of the fluting 56 in the shank 50. FIG. 6illustrates a standard endmill shank 60 having a contoured endmill flanksegment 62 set into one of three flank grooves 64.

In accordance with the present invention, one optional method of makinga contoured solid polycrystalline superabrasive material can includeproviding an electrically conductive polycrystalline superabrasiveblank. The polycrystalline superabrasive blank can be wireelectro-discharge machined to form a contoured solid polycrystallinesuperabrasive material having a predetermined shape. Wireelectro-discharge machining includes wire EDM, EDG, wire erosion, orother similar electrode erosion techniques. In this way, the blank canbe a freestanding polycrystalline superabrasive material which does notrequire a supporting substrate such as a carbide substrate. Relativelycomplex shapes and contours can be introduced into the polycrystallinematerial using such techniques. For example, endmill segments can be cutfrom an annular sleeve similar to sheath 24 of FIG. 4 where the segmentscan be cut directly from the sleeve with little or no excess material.Similarly, drill tip segments can be cut from a solid blank by curvedslicing of a PCD blank. A wire EDM machine is particularly useful formachining drill tip segments and endmill segments. In order toeffectively use wire EDM, the polycrystalline blank must be sufficientlyelectrically conductive to allow electro-discharge machining to occur.This can be accomplished by introducing conductive bonding medium and/orsintering aid into the presintered green body and then machining priorto any metal removal steps such as acid leaching

As previously stated, the present invention allows a number ofachievements in making shaped polycrystalline PCD or PCBN segments to beapplied for a variety of drilling and milling tools such as a tip forrotary diamond tools like drills, reamers, burrs, and endmills such asend- and face-milling tools such as flat bottom, ball nose, radius,inverted radius, and chamfer tools. First, a variety of grades of PCDcan be readily produced and thermally stable helical PCD tip can beproduced that is relatively unique in microstructure having improvedthermomechanical properties. Second, a desirable helical product shapefor higher performance can be readily obtained. Third, economics offurnishing a finished diamond tool of helical PCD cutting element isimproved. The improved price competitiveness comes from both a uniqueHPHT PCD process cell design and considerably simpler finishing(grinding/cutting) operations for a finished tool as compared to currentmethods of fabrication which are more labor intensive and includeexpensive finishing costs.

EXAMPLES

The following examples illustrate exemplary embodiments of theinvention. However, it is to be understood that the following are onlyexemplary or illustrative of the application of the principles of thepresent invention. Numerous modifications and alternative compositions,methods, and systems may be devised by those skilled in the art withoutdeparting from the spirit and scope of the present invention. Theappended claims are intended to cover such modifications andarrangements. Thus, while the present invention has been described abovewith particularity, the following examples provide further detail inconnection with what is presently deemed to be practical embodiments ofthe invention.

Example 1

A specially prepared diamond feed was made by granulation steps startedfrom a mixture of diamond having an average particle size of 20-45 μm,tungsten carbide powder of an average size of 2 μm and a cobalt powderof 1 μm in a content ratio of 75:20:5 wt %. This particulate mixture wascompacted, heated (including dewaxing and cementing), and then crushed.This specially granulated and crushed diamond feed was about 70 wt % of40-60 mesh composite particulates with a small percentage of 120/140mesh and −325 mesh particulates in 20 wt % and 5 wt %, respectively.

At the same time, a precursor assembly (similar to FIGS. 1 and 2),tantalum cup, salt bushing, graphite heater tube, and other inner/outercell parts of HPHT reaction cell were also prepared in a conventionalmanner to form a precursor assembly. The precursor of multiple helicalpartitions corresponding to drill tips was made of alumina that was of asintered grade for sufficient stiffness during HPHT processing. Thediamond feed was then premixed with the above composite granulateddiamond feed, a bonding medium, and binder in a 95:3:2 weight ratio andloaded into the preshaped openings of the precursor mold and closed withthe alumina cap (as in FIG. 2) to form an HPHT reaction cell.

The HPHT reaction cell with the loaded reaction cup assembly was placedin a conventional HPHT hydraulic press. The pressure was raised to about50 kb and then the temperature was elevated to around 1400° C. Afterbeing maintained for about 10 minutes, the temperature was lowered andthe pressure was gradually reduced. The resulting consolidated contouredhelical solid PCD discs were recovered from the cell.

Individual solid helical PCD discs were recovered from the cell bybreaking apart. Some of the pieces were not easily separated from theprecursor mold although the inner surface of the preshaped openings wascoated by HBN spray for improved detachment. Some of the PCD pieces wereslightly distorted such that those pieces will need minor grinding tocorrect the contoured shape. The individual solid helical PCD appear tobe good quality and typical shiny grey color PCD. Some of thesecontoured pieces were also acid treated partially or entirely in orderto remove the metal phases in between diamond grains depending on itsplanned utility.

Example 2

Example 1 was repeated with a specially prepared diamond feed but itsoriginal diamond feed powders were crushed PCD grits or particulatesrather than a typical fine diamond powder of Example 1. Both entirelyacid leached crushed PCD particulates and unleached crushed PCDparticulates were used in a diamond feed for these examples. Thepreparation of the final diamond feed and loading into the reaction cupassembly was made under the same procedures as in Example 1. Thesubsequent HPHT PCD sintering was also conducted as in Example 1. Thetwo types of solid contoured helical shape PCD discs were produced andboth materials exhibited the same grey and shiny color appearance ontheir surfaces.

One of contoured solid discs was shaped by typical grinding to clean theedges and was then vacuum brazed onto the tip of a twist drill (8 mmΦdrill rod) using a commercially available Ti—Ni—Au brazing alloy at1100° C. Of course, it is to be understood that the above-describedarrangements are only illustrative of the application of the principlesof the present invention. Numerous modifications and alternativearrangements may be devised by those skilled in the art withoutdeparting from the spirit and scope of the present invention and theappended claims are intended to cover such modifications andarrangements. Thus, while the present invention has been described abovewith particularity and detail in connection with what is presentlydeemed to be the most practical and preferred embodiments of theinvention, it will be apparent to those of ordinary skill in the artthat numerous modifications, including, but not limited to, variationsin size, materials, shape, form, function and manner of operation,assembly and use may be made without departing from the principles andconcepts set forth herein.

The invention claimed is:
 1. A contoured homogeneous solidpolycrystalline superabrasive segment having a helical non-planarsurface, which is a drill tip segment and is adapted for attachment to acutting tool wherein said segment is prepared by HPHT processing of ahomogeneous superabrasive particulate charge feed, and wherein thecontoured homogeneous solid polycrystalline superabrasive segment has apentagonal shape.
 2. A contoured segment according to claim 1 whereinthe polycrystalline superabrasive is a PCD or PCBN material.
 3. Acontoured segment according to claim 2 wherein a leading tip portion ofthe segment is a composite carbide material bonded to saidpolycrystalline superabrasive.
 4. A contoured segment according to claim3 wherein said composite carbide is tungsten carbide.
 5. A cutting toolcomprising a cutting tool substrate, which is a drill substrate, havingattached thereto a separately formed contoured homogeneous solidpolycrystalline superabrasive segment having a helical non-planarsurface, which is a drill tip segment, wherein said segment is preparedby HPHT processing of a homogeneous superabrasive particulate chargefeed, and wherein the contoured homogeneous solid polycrystallinesuperabrasive segment has a pentagonal shape.
 6. A cutting toolaccording to claim 5 wherein the contoured solid polycrystallinesuperabrasive segment is a PCD or PCBN material.
 7. A cutting toolaccording to claim 5 wherein the segment is attached to a correspondingcutting tool substrate by means of brazing.
 8. A cutting tool accordingto claim 5 wherein a leading tip portion of the segment attached to acutting tool substrate is a composite carbide material bonded to saidpolycrystalline superabrasive.
 9. A cutting tool according to claim 8wherein said composite carbide is tungsten carbide.
 10. A contouredsegment according to claim 1 wherein, wherein the contoured homogeneoussolid polycrystalline superabrasive segment is freestanding with nosubstrate.
 11. A contoured segment according to claim 1, wherein thecontoured homogenous solid polycrystalline superabrasive segment has asuperabrasive content of from about 90 vol % to about 98 vol %.
 12. Acontoured segment according to claim 1, wherein the homogenoussuperabrasive particulate charge feed is a bimodal charge feed.
 13. Acontoured segment according to claim 1, wherein the homogenoussuperabrasive particulate charge feed is a trimodal charge feed.
 14. Acontoured segment according to claim 1, wherein the homogenoussuperabrasive particulate charge feed comprises superabrasive sourceparticulates having a mesh size of from 40/50 mesh to 230 mesh.
 15. Acontoured segment according to claim 1, wherein the homogenoussuperabrasive particulate charge feed comprise superabrasive sourceparticulates having a particle size of from about 120 μm to about 200μm.
 16. A cutting tool according to claim 5, wherein the contouredhomogenous solid polycrystalline superabrasive segment has asuperabrasive content of from about 90 vol % to about 98 vol %.